CEA-Leti’s hybrid metrology project targets better R&D cycle times and yields at sub-28nm nodes

GRENOBLE, FRANCE: CEA-Leti, a leading global research center committed to creating and commercializing innovation in micro- and nanotechnologies, said today that its Hybrid Metrology Project has developed a way to reduce measurement uncertainty in the sub-28nm nodes.

The continuous shrinkage of IC feature dimensions has made measurement uncertainty one of the key factors to be controlled to guarantee sufficient production yield.

Researchers are challenged to get accurate measurements of sub-40nm dense trenches and contact holes coming from 193-immersion lithography or e-beam lithography. Top-down CD-SEM cannot provide profile information. Moreover, electron-material interaction (i.e., proximity effect, resist shrinkage phenomenon) leads to significant CD bias in the final measurements.

The Hybrid Metrology Project has shown noteworthy results in reducing measurement uncertainty at sub-28nm nodes using an alternative 3D-AFM (atomic force microscope) mode for CD measurement, the Deep Trench Mode. While traditionally this mode has been used for height measurement, it can be extended for certain applications to reach nanometer-scale accuracy of CD measurements employing certain optimized scan parameters.

The project’s research findings, which were presented at the SPIE Advanced Lithography Conference in San Jose, Calif., in February, also show significant limitations to aggressive trench-dimension measurements using the conventional 3D-AFM CD mode.

Hybrid metrology is related to the reference CD metrology feedback loop in conventional CD metrology process control that is mostly done by CD-SEM and scatterometry in fabs. Reference metrology is a means of accelerating R&D and cutting production costs, compared to CD-SEM and scatterometry techniques, through finer process window definition.

“The Hybrid Metrology Project puts CEA-Leti in a unique position of being able to help both equipment companies and chipmakers,” said Laurent Malier, CEO of CEA-Leti. “We anticipate helping equipment makers develop a CD metrology production tool dedicated to hybrid metrology that will reduce R&D cycle time and improve production yield for manufacturers.”

Project leader Johann Foucher, who presented the SPIE paper, said CD hybrid metrology potentially could be introduced in high-volume manufacturing for sub-28nm nodes. That would require hybrid metrology tools and software that will simplify the communication and optimization of complementary techniques to obtain a relevant and low-cost CD metrology configuration.

This hybrid metrology platform would facilitate and optimize data exchange between reference and production techniques. It decreases the number of measurement iterations as a function of accuracy control because it prevents introduction of residual errors due to poor accuracy of the initial production CD metrology technique.

CEA-Leti researchers found that by using a reference in-line CD technique such as CD-AFM, it is possible to replace most cross-section images currently done by scanning electron microscopy or transmission electron microscopy. The result is faster R&D cycle time for any kind of process control (lithography and etching).

For yield production, the final result is the same as for R&D because the accuracy lowers the total-measurement-uncertainty parameter and guarantees better CD uniformity and process window definition on a full wafer. The fabricated devices would have fewer performance variations from die to die, wafer to wafer and lot to lot, which results in higher production yield.

The Hybrid Metrology Project intends to develop all methodology and infrastructure needed to introduce hybrid metrology into high-volume manufacturing. It has already explored very advanced 3D-AFM tips that have been used with the enhanced Deep Trench Mode parameters, and ways of pushing the limits of 3D-AFM technology for measuring tight dimensions that could extend its capability for future nodes.